Is DART the solution?

Bangladesh is in need of planting the DART (Deep-ocean Assessment and Reporting of Tsunamis) system to mitigate losses due to tsunami. On September 13 in 2007, Bangladesh issued Tsunami alert in the coastal region of Bangladesh saying that Tsunami might hit the coastal parts of Bangladesh. After December 30 of that year, Bangladesh survived the effects of Tsunami, due to the natural barrier of its continental shelf stretching 200 km into the Bay of Bengal, reported the official Bangladesh News Agency.
The possibility of Tsunami depends on the distance from the earthquake which causes it. It also depends on how deep in the ocean the earthquake was. In Chittagong, the second largest city of Bangladesh, according to a newspaper report, in 1997 two high magnitude earthquakes occurred in a span of three days. This is unusual since earthquakes of such magnitude occur only about once a year on an average.
In the Bay of Bengal tides are the result of imbalanced, extraterrestrial, gravitational influences of the moon, sun, and planets. These waves were termed as "seismic sea waves" by scientists which is misleading. "Seismic" implies an earthquake-related generation mechanism but a tsunami can also be caused by a non-seismic events. In fact tsunamis are generated by landslides, volcanic eruptions, explosions, and by the impact of cosmic bodies, such as meteorites besides underwater earthquakes. These disturbances cause the seabed to move swiftly and shift a large amount of water and disrupt the sea surface.
During the NUS-TMSI workshop on "Earthquake and Tsunami" held in 2007 concern was raised and discussed that the DART project should be immediately implemented. The proposed sea area is seen in fig 01.
The information collected by a network of DART systems positioned at strategic locations throughout the ocean plays a critical role in tsunami forecasting. When a tsunami event occurs, the first information available about the source of the tsunami is based only on the available seismic information for the earthquake event. As the tsunami wave propagates across the ocean and successively reaches the DART systems, these systems report sea level information measurements back to the tsunami warning centers, where the information is processed to produce a new and more refined estimate of the tsunami source. The result is an increasingly accurate forecast of the tsunami that can be used to issue watches, warnings or evacuations.
Several numerical tsunami models have been developed in the past, which can describe reasonably well the tsunami propagation in Deep Ocean, once the source region information is properly provided. These numerical models can estimate the direction of tsunami propagation and the wave height distribution from the source region to the near shore areas. Based on these numerical models, several frameworks for establishing tsunami hazard mitigation programmes and early tsunami warning systems have been discussed and proposed.
Proposed Initiative addresses:
1) Source parameter identification: Numerical modeling of tsunamis will not be useful for assessing tsunami hazards unless reliable input data are available, which include earthquake source parameters (epicenter, depth, magnitude, rupture plane surface area, dip angle, slip angle and strike angle) and accurate bathymetry database.
* Collect and analyse seismograms and earthquake data so that earthquakes in this region can be systematically relocated and the focal mechanisms re-determined using the latest seismological methods and techniques.
* Survey and collect bathymetry data along the trenches for improving the accuracy of modeling tsunami generation.
* Develop better tsunami generation model to include the effects of horizontal seafloor displacements and landslides.
2) Validation and development of accurate and reliable tsunami simulation models
Several numerical models describing tsunami propagation and inundation have been developed that can provide reliable estimates of tsunami arrival times.
* Establish benchmark problems to determine the accuracy of these simulation models for calculating near shore hydrodynamics including tides, breaking waves, bottom friction, overland flows, flow-structure interactions, and the resonated motions in a semi-enclosed region such as a bay.
* Survey and collect bathymetry and topography data in the coastal zones around the Bay of Bengal
* Survey and calibrate existing tide gages and install new near shore sea water level sensors.
* Develop a comprehensive tsunami modeling system, probabilistic and statistical approaches to estimate tsunami potentiality and impact.
3) Development of tsunami early warning system and fast tsunami forecasting: Since limited resources will be available for installing and maintaining deep water sensors, it is important to develop a scientific methodology for determining the optimal locations of these future sensors. Moreover, for an accurate and fast tsunami forecasting, once a tsunami is detected by a sensor, an algorithm needs to be developed to ensure in two ways:
* Design an algorithm for an early tsunami warning system by determining where and how many sensors to install. The goal of Sensor Optimal Placement algorithm is to identify the best location for deepwater sensors and to give ample warning time.
* Design an algorithm for fast forecasting of tsunami using data detected by deepwater sensors. Although a procedure for tsunami forecasting using the senor data has been established by warning system.
4) Tsunami coastal effects and hazards mitigation programs
* Develop new inundation metrics for inundation maps that account for wave heights, velocities and force indices.
* Develop design guidelines for coastal structures to improve their resistance/resilience.
* Implement probabilistic hazard analysis into the inundation maps.
Public awareness should be raised in this regard. Government and non-government authorities should extend their helping hands to promote DART in Bay of Bengal to reduce TSUNAMI LOSSES.

The writer is a Graduate of NUS (National University of Singapore).